1. Technical Field of the Invention
The present invention relates generally to an optical object detecting apparatus such as a laser radar designed to emit and sweep a laser beam through a selected one of light-emitting windows and to receive a return of the laser beam from an object to produce data on the type of and/or distance to the object.
2. Background Art
FIG. 12(a) shows a conventional automotive laser radar designed to emit laser beams intermittently over an angular range embracing an automobile and receive a return of the laser beam to detect a reflective object. This type of radar may be used with an optical distance measuring system designed to measure the mount of time required by the laser beam to travel to and return from an object to determine the distance to the object.
It is advisable for such distance measuring systems to obtain two-dimensional information about a target over a wider range, that is, to broaden an area scanned by laser beams for increasing a detectable range. The broadening of the scan area, however, requires changing a direction of emission of the laser beam two-dimensionally. Specifically, both a lateral scan mechanism working to sweep the laser beam over a lateral angular range in a width-wise direction of the automobile and a vertical san mechanism working to sweep the laser beam over a vertical angular range in a height-wise direction of the automobile are needed, thus resulting in a complex structure of the system. For example, in a case where the laser beam is swept by a reflective mirror such as a polygon mirror 106, as shown in FIG. 12(b), it needs a complex bi-directional rotary mechanism working to rotate the polygon mirror 106 in the width-wise and height-wise directions of the automobile.
In order to avoid the above problem, Japanese Patent First Publication Nos. 2000-56018 (equivalent to U.S. Pat. No. 6,301,003 B1 assigned to the same assignee as that of this application) and 7-198850 teach a distance measuring apparatus capable of acquiring two-dimensional information about a target using a simple control mechanism. The acquisition of the two-dimensional information is achieved by scanning a laser beam one-dimensionally and at the same time selectively activating light-sensitive cells according to the location of the target in a direction (i.e., a height-wise direction of the vehicle) perpendicular to the scanning direction. Specifically, the apparatus works to shape the laser beam so as to have a rectangular cross section covering a selected vertical angle of a total laser-emitting range (i.e., a radar detectable range) and swing it only in a lateral direction (i.e., the width-wise direction of the vehicle). The apparatus performs the scan in the lateral direction several times and selectively activates the light-sensitive cells every scan, thereby determining the distance to the target.
The above type of laser radar requires increasing a vertical view and a maximum measurable distance in order to continue tracking a preceding vehicle (i.e., a target) correctly even if the preceding vehicle or the radar itself undergoes vertical movements arising from undulations of a road, for example. The increasing of the vertical view requires increasing a vertical range of emission of the laser beam, that is, increasing the size of the cross section of the laser beam in the vertical direction. The increasing of the size of the laser beam, however, results in a drop in emission power density thereof, which leads to a decrease in distance measurable range. Assuring a desired distance measurable range requires an increase in power consumption of the apparatus.
The two-dimensional scan system is capable of tracking the preceding vehicle easily even if it moves vertically, but however, needs to process data about the whole of the radar range, thus resulting in an increase in operating load of the system.
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide an optical object detecting apparatus such as a laser radar capable of scanning a required minimum area through one-dimensional mechanical scans of light to track an object accurately even if it has moved vertically without bringing about increases in operational load and power consumption of the apparatus.
According to one aspect of the invention, there is provided an object detecting apparatus which may be used as an automotive anti-collision system. The object detecting apparatus comprises: (a) a laser emitter emitting a laser beam; (b) a laser scanner designed to swing the laser beam emitted from the laser emitter in a first direction in a cycle within a given object detection zone, the laser scanner being also designed to move in a second direction substantially perpendicular to the first direction, the laser beam having a cross section which is elongated in the second direction so as to scan an area selected within the object detection zone in one scan cycle; (c) a light-sensitive sensor, when activated, sensitive to a return of the laser beam from a reflective object present in the object detection zone to produce a signal for acquiring given information on the object, the light-sensitive sensor including a plurality of light-sensitive cells arrayed adjacent to each other in the second direction; (d) a selecting circuit working to select ones of the light-sensitive cells to be activated in sequence one in each scan cycle of the laser beam; and (e) an area shifting circuit working to determine a position of the object in the second direction within the selected area using the signal outputted from the light-sensitive sensor and move the laser scanner to shift the selected area in the second direction within the object detection zone based on the position of the object.
In the preferred mode of the invention, the laser emitter includes a multi-stripe semiconductor laser which has a plurality of discrete light-emissive areas formed in a single emission layer. The light-emissive areas is activatable to emit laser beams, respectively, which has a total sectional area elongated in the second direction so as to scan the area selected within the object detection zone in each scan cycle.
The apparatus further comprises a distance determining circuit working to measure a time the laser beam takes to travel to and return from the object to determine a distance to the object.
The selecting circuit switches between the light-sensitive cells every scan cycle of the laser beam.
The selecting circuit works to select a given number of the light-sensitive cells corresponding to the area selected within the object detection zone to be activated, one for each scan cycle of the laser beam.
The area shifting circuit works to move the laser scanner to shift the selected area in the second direction within the object detection zone so as to acquire the object at a fixed position within the selected area at all times.
According to the second aspect of the invention, there is provided an object detecting apparatus which comprises: (a) a laser emitter emitting a laser beam; (b) a laser scanner designed to swing the laser beam emitted from the laser emitter in a first direction in a cycle within a given object detection zone, the laser scanner being also designed to move in a second direction substantially perpendicular to the first direction, the laser beam having a cross section which is elongated in the second direction so as to scan an area selected within the object detection zone in a single scan cycle; (c) a light-sensitive sensor, when activated, sensitive to a return of the laser beam from a reflective object present in the object detection zone to produce a signal for acquiring given information on the object, the light-sensitive sensor including a plurality of first arrays of light-sensitive cells aligned in the first direction and a plurality of second arrays of light-sensitive cells aligned in the second direction; (d) a selecting circuit working to selecting a given number of the light-sensitive cells to be activated in each scan cycle of the laser beam; and (e) an area shifting circuit working to determine a position of the object in the second direction within the selected area using the signal outputted from the light-sensitive sensor and move the laser scanner to shift the selected area in the second direction within the object detection zone based on the position of the object.
In the preferred mode of the invention, the apparatus further comprises a distance determining circuit working to measure a time the laser beam takes to travel to and return from the object to determine a distance to the object.
The area shifting circuit works to move the laser scanner to shift the selected area in the second direction within the object detection zone so as to acquire the object at a fixed position within the selected area at all times.
According to the third aspect of the invention, there is provided an object detecting apparatus which comprises: (a) a laser scanner designed to swing a laser beam in a first direction in a cycle within a given object detection zone, the laser scanner being also designed to move in a second direction substantially perpendicular to the first direction; (b) a laser emitter including laser emitting elements arrayed in the second direction, each of the laser emitting elements working to output a laser beam to the laser scanner; (c) a light-sensitive sensor sensitive to a return of the laser beam from a reflective object present in the object detection zone to produce a signal for acquiring given information on the object; (d) a selecting circuit working to switch between the laser emitting elements of the laser emitter in the second direction in each scan cycle of the laser beam; and (e) an area shifting circuit working to determine a position of the object in the second direction within the selected area using the signal outputted from the light-sensitive sensor and move the laser scanner to shift the selected area in the second direction within the object detection zone based on the position of the object.
In the preferred mode of the invention, the apparatus further comprises a distance determining circuit working to measure a time the laser beam takes to travel to and return from the object to determine a distance to the object.
The laser emitter includes a multi-stripe semiconductor laser.